Nowadays a demand for development of a communication system for performing communication with a communication object, to which this system is brought close to such an extent that this system contacts or closely contacts the communication object (concretely, which is positioned in the proximity area within a distance of almost 10 cm or less where an electric field or a magnetic field can act), by utilizing an electric field or a magnetic field (referred to as a “proximity noncontact communication system” hereinafter) is growing. In other words, this communication system can be used in such a manner that electric data in which personal information, e.g., data such as a phone book, or the like are stored are copied into a cellular phone; an electronic medical chart is read/written in a hospital, a pharmacy, or the like; electric resident's register data of a certificate of residence, a family register, or the like is read/claimed, or the like; personal hobby data (various data such as music, image, and the like) are transferred/copied/stored in user's own cellular phone, or the like; money data is input into a desired electronic device as a prepaid money for a vending machine, or the like; money data is used as a pass to pass a gate in an amusement park, a station, or the like, and others. For this purpose, a development of a mobile communication device having a proximity noncontact communicating function has been variously discussed. This function makes it possible for the user to perform the proximity noncontact communication with a proximity noncontact communication equipment on the outside (referred to as an “external proximity noncontact communication equipment” hereinafter), a proximity noncontact communication card on the outside (referred to as an “external proximity noncontact communication card” hereinafter), or the like as the other end of the proximity noncontact communication.
As one of the mobile communication devices that are compatible with such proximity noncontact communication system, a development of the cellular phone to which a proximity noncontact communicating function is attached is proceeding. For example, FIG. 6 shows a circuit of a proximity noncontact communication portion 100 in the cellular phone to which a proximity noncontact communicating function is attached. Since this proximity noncontact communication portion 100 is constructed by one antenna 101 such that respective frequency bands overlap each other when the proximity noncontact communication is held between the cellular phone and the external proximity noncontact communication equipment and the external proximity noncontact communication card (both not shown), two functions for the external proximity noncontact communication equipment and the external proximity noncontact communication card can be provided while taking account of a miniaturization of the cellular phone.
Here, when the proximity noncontact communication is held between the external proximity noncontact communication equipment and the cellular phone, the proximity noncontact communication portion 100 installed into the cellular phone serves as a card. In contrast, when the proximity noncontact communication is held between the external proximity noncontact communication card and the cellular phone, the proximity noncontact communication portion 100 installed into the cellular phone serves as a reader/writer.
Also, control of the proximity noncontact communication is largely different between the card function and the reader/writer function. Therefore, as shown in FIG. 6, the card function and the reader/writer function are controlled separately by a proximity noncontact communication controlling portion (proximity noncontact communication IC) 110 that executes operation control respectively, and also connection terminals of the antenna 101 are provided separately. As a result, even though the antenna 101 is constructed as a single unit, a connection of the antenna 101 must be switched to respond to respective functions and also a switch 102 and a switch 103 must be provided.
By the way, these switches 102, 103 must be arranged in series with the proximity noncontact communication antenna 101 and the proximity noncontact communication controlling portion (proximity noncontact communication IC) 110. At that time, such a problem existed that an available distance in the proximity noncontact communication is shortened by the influence of the series-inserted switches. Therefore, an approach for extending the available distance by enlarging an area of the antenna may be considered. In this case, such a problem existed that a size of the mobile communication device itself is also increased when the area of the antenna is enlarged.
For this reason, the proximity noncontact communication system in which the antenna is provided separately to the external proximity noncontact communication equipment and the external proximity noncontact communication card respectively and a size reduction of the antenna can be attained by forming two antennas on the same plane is developed variously (see Patent Literature 1, for example).
As one of the mobile communication devices that are compatible with such proximity noncontact communication system, a development of the cellular phone to which the proximity noncontact communicating functions shown in FIG. 7 to FIG. 9, for example, are attached is examined. As shown in FIG. 7, the cellular phone having a straight main case 201 (of course, a folding type may be employed) and equipped with a cellular phone antenna 202 and a proximity noncontact communication antenna 203 (constructed by external proximity noncontact communication equipment antennas 203A, 203B) has been proposed. This cellular phone antenna 202 is provided in the main case 201 to transmit/receive the data to/from a base station (not shown). This proximity noncontact communication antenna 203 is provided near one surface (upper surface in FIG. 7 and FIG. 8) of the main case 201 to perform the proximity noncontact communication with an external proximity noncontact communication equipment 300. Also, this external proximity noncontact communication equipment 300 acting as the other end of the proximity noncontact communication with a cellular phone 200 is equipped with a proximity noncontact communication antenna 301.
Also, as shown in FIG. 8, the cellular phone that performs the proximity noncontact communication with an external proximity noncontact communication card 400 via a proximity noncontact communication antenna 401 has been proposed. This proximity noncontact communication antenna 401 is provided to the external proximity noncontact communication card 400 to establish the proximity noncontact communication with this cellular phone 200.
In this manner, the cellular phone 200 having a proximity noncontact communicating function of transmitting/receiving phone conversation or data communication to/from a base station via the cellular phone antenna 202. Meanwhile, when the proximity noncontact communication is established between the external proximity noncontact communication equipment 300 and the external proximity noncontact communication card 400 and the cellular phone 200, the external proximity noncontact communication equipment antennas 203A, 203B are brought into contact with or held closely to the external proximity noncontact communication equipment 300 and the external proximity noncontact communication card 400. Thus, the proximity noncontact communication is established between the external proximity noncontact communication equipment antenna 203A and the proximity noncontact communication antenna 301 in the external proximity noncontact communication equipment 300 or between the external proximity noncontact communication equipment antenna 203B and the proximity noncontact communication antenna 401 in the external proximity noncontact communication card 400.
Also, the proximity noncontact communication antenna 203 whose antennas 203A, 203B are formed on the same plane is studied.
As shown in FIG. 9, the external proximity noncontact communication equipment antenna 203A is connected to a first antenna tuning capacitor 206A via connection terminals 204A, 205A. Also, the external proximity noncontact communication equipment antenna 203A is connected to second antenna tuning capacitors 207A, 208A through respective connection terminals, and is also connected to the controlling portion 110 for controlling the proximity noncontact communication.
In contrast, the external proximity noncontact communication card antenna 203B is connected to a first antenna tuning capacitor 206B via connection terminals 204B, 205B. Also, the external proximity noncontact communication card antenna 203B is connected to second antenna tuning capacitors 207B, 208B through respective connection terminals, and is also connected to the controlling portion 110 for controlling the proximity noncontact communication.    Patent Literature 1: JP-A-2004-364199